Apomorphy

A derived trait distinct to a certain species or group in a phylogenetic tree down to its descendant. Any amount of change denotes the basis oftaxonomy since each group of animal have a unique character and if most likely showed various apomorphies entails the nearest related links.

Supplement

An apomorphy that is limited to a single species is termed an autapomorphy. Any associations of these single species cannot provide exact information though it point out the level of divergence from its nearest links.

This is an evolutionary innovation thus it is a concept which has meaning only in a particular framework that shows evidence for the existence of a group attributes in a shared common evolutionary history.